The objectives of the proposed research will be to define the physiologic and biochemical factors inherent in glucagon release in both the normal and diabetic rat pancreas. More specifically it is the goal of this proposal to seek answers to the following questions: 1) What are the major physiologic factors that control glucagon secretion and what are the specific defects in the alpha cell of alloxan and streptozotocin diabetic rats which result in pathologically elevated glucagon levels; 2) What are the biochemical mechanisms resulting in glucose suppression of alpha cell function and what role, if any, does insulin have on inhibition of glucagon secretion; 3) What are the changes in intermediary and cofactor metabolism which occur in the alpha cell, as compared to the adjacent beta cell when challenged with physiologic substrates (i.e. glucose, amino acids, and fatty acids) which are known to modulate release of both insulin and glucagon; 4) Is the alpha cell freely permeable to glucose (as is the beta cell) or is there an insulin requiring transport system for glucose and finally; 5) Is release of glucagon dependent upon metabolic changes within the alpha cell or rather primarily regulated by substrate receptors on the external surface of the alpha cell? With the availability of collaborative facilities which allow for simultaneous investigation of immunoreactive insulin and glucagon release from in vitro preparations (i.e. isolated perfused rat pancreas, incubated islets and perifused islets) together with the capability of microanalysis of metabolites and cofactors within alpha cell islets and islets containing the mixed population of cells, we feel that the fundamental mechanisms controlling release of both insulin and glucagon can now be elucidated. We will accomplish the above by: (1) Application of metabolic inhibitors to dissect out the minimal requirements for glucose modulation of alpha cell function; (2) performing structure-activity studies will glucose analogues and derivatives to elucidate the molecular basis of glucose suppression of alpha cells; and by (3) measuring metabolite and cofactor levels in freeze dried preparations of alpha cell islets from diabetic rats and correlating glucagon release with metabolic changes.